Stabilized polymeric composition



United States Patent US. Cl. 260897 5 Claims ABSTRACT OF THE DISCLOSURE The specification describes stabilizers for polymers, particularly polypropylene, that are subject to coppercatalyzed oxidation. The adverse effects due to the presence of copper in the polymer are reduced by adding to the polymer a small amount of oxamide or a derivative thereof. Standard antioxidants are included also.

This is a continuation of application Ser. No. 349,784, filed Oct. 1, 1963, which is a division of application Ser. No. 77,012, filed Dec. 20*, 1960 by Ralph H. Hansen and Charles A. Russell, both now abandoned, and relates to stabilized polymeric compositions. Further, it concerns the stabilization of polypropylene and higher order polymerized saturated hydrocarbon alkenes against oxidative degradation.

Much attention has recently been directed to the stabilization of polyethylene. It now appears that various of the higher order saturated hydrocarbon polymers are better adapted for certain uses. Specifically, polypropylene appears to be particularly promising for expanded wire insulation. It is tough, hard, sufiiciently flexible, resistant to thermal embrittlement and stress cracking, high melting and quite insoluble in many ordinary solvents. However, accompanying these advantages are various factors hindering the use of these materials, notably their propensity toward thermal oxidation. These higher order polymers are easily oxidized due to the relatively high proportion of tertiary carbon atoms they contain in comparison with the almost linear materials such as the high density polyethylenes. Further, thermal oxidation of these higher order polymers is catalyzed by metal ions. In view of this propensity toward thermal oxidation and the susceptibility to metal ion catalysis, the problem of oxidative degradation has been found to be severe in these higher order polymers. Specifically, it has been found that the useful life of polypropylene, even when stabilized with the best known antioxidant materials, becomes commercially prohibitive for many applications when used in contact with copper. As primary electrical insulation for copper wires and cables, for instance, polypropylene becomes useless after a very few months. Accordingly, this invention is directed to the stabilization against thermal oxidative degradation accelerated by the presence of copper ions.

This invention proposes a new stabilized composition effective against oxidative degradation promoted or accelerated by contact with copper ions. Higher order polymers, stabilized with the novel components of this invention, show a high degree of stability both in contact and out of contact with copper. The constituents of the stabilized system according to this invention includes a higher order polymer, for instance, polypropylene, an inhibitor against copper catalyzed oxidative breakdown and an antioxidant.

3,462,517 Patented Aug. 19, 1969 The polymers intended to be within the scope of this invention are polypropylene and higher order polymers. The term higher order polymers refers to polymers of more complex hydrocarbons, i.e., those having more than three carbon atoms. Some specific compounds appropriate for this invention are polypropylene, polybutene-l, poly-3-methyl butene-l, poly-4-methyl pentene-l, poly- 4,4-dimethyl pentene-l, polydodecene-l, and poly-3- methyl pentene-l. Mixture of these compound and copolymers thereof are also intended to be included as part of the polymeric class adapted to be stabilized by the composition of this invention. For the purposes here a mixture is considered to be within the scope of this invention as long as the predominant portion of its composition is a polymer of the character as herein defined.

It is also intended that this invention encompass polymeric compositions containing minor proportions of additional ingredients such as fillers, coloring agents, inhibitors against ultraviolet degradation such as carbon black, etc. Of particular concern in this connection are com pound capable of expanding the polymer. As was stated previously, expanded polypropylene, if properly protected agianst copper poisoning with the inhibitor of this invention, is an excellent electrical insulation material. Expanded polymers serve other well known uses and are attractive because of their reduced cost. The stabilizing composition according to this invention is fully compatible with known commercial blowing agents and will not interfere with their blowing action.

The novel inhibitors against copper ion catalized oxidative degradation according to the primary feature of this invention are certain compounds derived generally from oxamide which contain the radical It has been found that certain of these compounds possessing at least this basic structure provide good inhibiting effects in the polymers previously defined. The specific compounds intended to be within the scope of this invention are defined as follows:

Oxamide; polymers and copolymers of oxamide and derivatives thereof; derivatives of oxamide having the general formula;

where R is either an ethylene or a keto group; and derivatives of oxamide having the general formula:

where R and R are cyclic radicals. R and R may be the same or different. They may be homocyclic, heterocyclic, aromatic or polycyclic and may have 4-6 carbon atoms in each cyclic ring.

In each of the latter two cases, R, R and R may be substituted in any manner as desired. The compounds falling within the scope of this invention are any which contain these basic structures as set forth above.

The following examples are offered to show that compounds having the structure defined above will be effective inhibitors when used according to the prescribed teachings of this invention. Each example gives a particular polymeric composition including the inhibitor of the class defined and additionally including a particular well known stabilizer against thermal oxidation. Each example gives the results of an accelerated oxidation test whereby the effective useful life of the polymer is measured. In every case the time in hours is that period during which the polymer retains its useful properties. According to this accelerated test procedure, it has been found that the point at which the polymer has effectively failed is that where the polymer has absorbed oxygen in the amount of 10 cc./gram of sample. Accordingly, each the sample in a closed system was measured volumetrically, were carried out at a temperature of 140 C. The reaction vessels consisted of Corning No. 459,050 oxygen uptake pipets. Approximately 30 inches of transparent plastic tubing, used as a leveling tube, was attached, and

result reported is considered a measure of the failure 5 the appropriate amount of mercury was added by filling point of the particular composition listed. As will be through the plastic tubing. The tubing was clamped to seen the group of materials tested as inhibitors represents restrict the flow of mercury and an inner tube, which a reasonable cross-section of the compounds falling withcontained the sample and enough Linde Type 5-A M0- in the general class of oxamide and the derivatives delecular sieve (a zeolite resin) to absorb the CO and fined above. H O evolved during oxidation, was added. The sample The accelerated aging tests were conducted substanwas comprised of strips of 10-mil molded film or extially as follows: panded wire insulation, wire and all (about 8-10 mils of Samples of the polymer containing the additives as about 55% plastic content on 19 gauge wire). indicated in each example were prepared in a Brabender In both cases, the weight of the plastic sample used Plastograph. The Brabender was heated to 205-210 C. was 0.1 gram. The pipet was then sealed under a steady A charge of 30 grams of resin was placed in the chamber flow of oxygen after first alternately evacuating and flushand warmed for 3 minutes under a nitrogen atmosphere. ing with oxygen several times. The sealed pipet was then The additives as desired were then added in amounts of placed into a constant temperature bath maintained at .5% antioxidant and inhibitor and 1.4% copper in the 20 the desired temperature and an initial volume reading form of copper dust. This mixture was then mixed for was taken after about 15 minutes. The rate of reaction seven minutes. was followed by observing changes in the level of mercury The copper dust used was prepared as follows: in the sample pipet as compared with a control pipet Purified electrolytic grade copper was heated to a bright (prepared in the same way except that it did not contain red color in the reducing flame of a bunsen burner. the polymer sample). While still bright red, the copper was quickly plunged It has been noted that the physical properties (as into a beaker containing absolute alcohol. The alcohol evidenced by brittleness, lack of elongation, etc.) of polywas decanted and the copper dust was dried in a vacuum propylene specimens deteriorated markedly after an oxyoven for a minimum of 2 hours at 60 C. The freshlygen uptake of 10 cc. per gram of polymer. Accordingly, reduced copper was removed from the oven and the time for failure of a test specimen is reported as the time resultant clumps were broken up and added to the olywhen thermal oxidation has proceeded to this extent. mer where desired. The results of the accelerated aging tests on various The batch was then removed from the chamber, compositions including oxamide type inhibitors are conpressed flat to about 100 mils, and a portion molded in a tained in the following table. The polymer in Examples polished aluminum picture frame mold to a thickness of 1 16 wa polypropylene, Examples 17-20 directed to the 10 mils. Molding was accomplished at a temperature of use f p01y(butene-1) e in l ded to how th adaptaabout 175180 C. and a pressure of between 1200 a bility of this invention to higher order polymers, In Ex- 2000 psi. The sample was kept at this temperature and amples 21-23 the polymer was polypropylene expanded pressure for 1 minute and then the mold was transferred ith a kno commercial blowing agent, azodicarbonto a cold press for cooling under pressure. amide and additionally including approximately 10% of The extruded samples reported were prepared from a polyisobutylene. These latter examples show the effecpolypropylene composition containing about 10% of tiveness of the stabilizer compositions of this invention in polyisobutylene and 0.5%. polymer mixtures which contain a predominant portion 4,4 thiobis-(3-methy1-6-tert.-butyl-phenol). Granules f olypropylene r higher order polymers. of the P y Were Shaken With 0f the desired In each example listed the second through fifth columns hibitor. The mixture was then extruded on a productiond fi th o ition te ted by the ro edure o tlined size extruder. This resulted in about 8-10 mils of exabove. The last column sets forth the effective period panded insulation (40-50% voids) on 19 gauge copper of inhibition at 140 C. as discussed previously. The sigwire. nificance of these periods in terms of predictable effec- Accelerated thermal oxidation tests, in which th tive life in actual anticipated use Will be treated hereinamount of oxygen reacting at atmospheric pressure with after.

TABLE I Useful Lite on Metal Ion Accelerated Example Polymer Added .5% Thermal Antioxidant .5% Inhibitor Basis (Hours) 1 Polypropylene None None None 1.2 2.- .do -do. 4-th1obis-(3-methyl-6- 440 tert.butyl phenol) do 43 dc. 78 do. Poly-(Ltrdiaminohexane)-oximide 105 .do Poly-[1,4-bis(aminomethyl), cyelohexyl] oxirnlde. 141 do.. Poly-(3,3-diaminodipropylamine) oximide Cu .do Poly-[0.75 1,4-bis(aminomethyl)cyclohexyl0.25 1,6-di 107 hexane] oximide. Ethylene oxamide 1133 56 135 76 06 73 do 0 Poly(butene-1) None 1.0 do do 4,4-thiobis-(3-methyl-6- 350 tort.butyl phenol) d o 170 N,N-diphenyl oxamid 250 Oxamide 82 N,N-dipheny1 oxamide 23* ..do Cu. do None 43 "Polymer expanded with 0.5% azodicarbonamide and includes 10% polylsobutylene.

5 6 Examples 1 (polypropylene) and 17 (poly( butene-l)) this invention was added and the effective life again show the effective life of the pure virgin unihibited polymeasured. The data obtained is as follows:

TABLE II Useful Life on Metal Ion Accelerated Example Polymer Added .5% Thermal Antioxidant .5% Inhibitor Basis (hours) Polypropylene None None 1.2 .do .do (1 30 0.5 12 372 d 52 Cu d 112 -N-pentadecy1 resorcinol- N 1?: so 106 14 o 100 .5% 423 .5% poly-trimethyl dihydroquinoline. 38 do Cu d0 .do 185 Cu.... do N,N-diphenyloxamide 292 None. 4-4'-butylidenebis-(6-tert.-butyl3-methyl None 77 phenol). Cu do do 9 42 ..do C11 ..do N,N-diphe11yl oxemide 47 mer. Examples 2 and 18 show the increase in effective It is readily apparent that in the case of each of the life of the polymer (on accelerated basis) after stabilizafive known commercial antioxidant materials tested, the tion with .5% of 4,4'-thiobis-(3-methyl-6-tert.-butyl-pheeffective life of the polymer when in contact with copper 1101), a typical known commercial antioxidant. All perwas significantly increased by the addition of an oxamide centage compositions used here and elsewhere in this type compound of the class defined previously. Thus it specification are percentage compostion by weight. Exis seen that the oxamide type inhibitors of this invention amples 3 and 19 indicate the drastic reduction of the efare effective when used in conjunction or combination fective life of the polymer stabilized with an ordinary with any known effective antioxidant material. antioxidant when placed in contact with copper. How- The amount of the inhibitor added maintains its efever, Examples 4-16 (polypropylene) and 20 (poly(bufectiveness as long as it does not significantly depart from tene-1)) illustrate the increased stabilization exhibited by the range of .1% to 5%. In decreasing the amount below polymers which already include a commercial antioxidant .1%, the inhibitor is found to lose effectiveness. Amounts (4,4'-thiobis-(3-methyl-6-tert.-butyl-phenol) through the over 5% have been found to be effective but no advanaddition of .5 of an inhibitor of this invention contage is obtained through the use of larger amounts. Containing the oxamide radical. It is readily apparent from sequently, it is economically unfeasible to include the inan examination of the effective periods indicated in Table hibitors in amounts greater than 5%. The amount of I that polymers containing the mixture of this invention antioxidant required is dependent in part on the degree provide far superior stability against thermal oxidation 40 of effectiveness provided by various percentages of difin the presence of copper than can be obtained through ferent antioxidants and, of course, the degree of effecthe use of commercial antioxidants alone. Examples 21- tiveness desired. Amounts in the range of .05 to 5% 23 are directed to an expanded polymer extruded by are generally recommended for any of the commonly known techniques onto 19 gauge copper wire and intended known antioxidant materials.

for use as primary electrical insulation. The thickness of The significance of the accelerated aging studies in the polymer insulation was in each case about 0.010" terms of effective useful life under actual service condiand the expansion was accomplished by the use of 0.5% tions are found by extrapolating the effective period in azodicarbonamide and initiated at approximately 200 hours obtained at 140 C. as set forth in the tables to C. The polymers in Examples 21-23 additionally included the expected life at the temperature designated for serv- 10% poly-(isobutylene) to improve strength and to reice use through an Arrhenious plot obtained at at least duce low temperature brittleness. These examples are in- 2 other temperatures. This method of interpreting accluded to show that the stabilizing mixture of this invencelerated test data is well known in the art and is necestion is applicable to mixtures of polymers and does not sary to prescribe or predict service performance in varinterfere with commercial blowing agents used in expandious desired uses. The extrapolated data for a typical ing the polymer. As stated previously the stabilizers of stabilized polymer of this invention indicates that an this invention are of particular interest for use in expanded efiective period of stabilization in accelerated tests of 75 polymeric primary electrical insulation over copper wire hours at 140 C. will provide an effective stabilization which requires that the blowing or expanding agents and period at 70 C. of 30 years. the stabilizing agents be compatible. Variations and modifications of the stabilizing composi- To illustrate that the stabilizing mixture of this invention of this invention will become apparent to those tion is effective regardless of the particular commercial skilled in the art. However, all such departures from this antioxidant chosen, a series of examples are presented specification as are properly considered within the skill in Table II. Example 24 is included as a control showing of the art and also within the basic concepts of the adpure uninhibited polypropylene. The experimental procevance provided to the art by this invention, are to be also dure was identical to that used in the previous examples. properly considered within the scope of this invention as The headings on the columns of data appearing in Table defined by this specification and the appended claims.

II are the same as those column headings appearing in What is claimed is:

Table I. In each of Examples 25, 28, 31, 34, 37 and 40, 1. A polymer composition comprising: polypropylene a different commercial antioxidant was added to the pure stabilized against oxidation with a stabilizing amount of polymer and the degree of eflfectiveness was measured and 7 a thermal antioxidant, a contaminating amount of coprecorded in the last column of Table II. In Examples 26, per ions tending to promote oxidation even in the pres- 29, 32, 35, 38 and 41, copper dust was added to the otherence of the said thermal antioxidant, and a copper inwise stabilized polymer and the reduction in effective hibitor in an amount of approximately 0.1 percent to life was noted. In Examples 27, 30, 33, 36, 39 and 42 a 5 percent of the total composition for reducing the ad.- typical inhibitor according to the principal teachings of verse effects of the copper ions present, the copper inhibitor selected from the group consisting of compounds having the general formula:

HOOH Ill ll where R and R are cyclic radicals, compounds having the general formula:

Mi t R Where R is an ethylene or keto radical, and polymers of monomers containing the radical:

3. The composition of claim 1 in which the copper inhibitor is a compound having the general formula: I? I R1N-C( )NRz where R and R are benzyl or phenyl groups.

4. The composition of claim 1 in which the antioxidant is 4,4'-thiobis-(3-methyl-6-tert. butyl phenol).

5. The composition of claim 1 in which the polymer contains 10 percent poly-(isobutylene) and percent polypropylene.

References Cited UNITED STATES PATENTS 2,683,132 7/1954 Young et al. 26045.9 2,857,424 10/1958 Cox 260-459 2,993,028 7/1961 Randalli 260-897 2,997,455 8/1961 Broich et al 260-459 3,121,068 2/1964 Baum 260 -897 2,945,838 7/1960 Prober 26045.9 3,160,680 12/1964 Tholstrup et al. 260-897 SAMUEL H. BLECH, Primary Examiner C. I. SECCURO, Assistant Examiner US. Cl. X.R. 

